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Chapter 8 Muscles. Pages: 178-183. Introduction. Muscles are made up of three types of tissues: Skeletal (focus of chapter) Smooth Cardiac. Structure of a Skeletal Muscle. Muscular System is made up of: Individual muscles (organs) Which are made up of - PowerPoint PPT Presentation
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CHAPTER 8 MUSCLES
Pages: 178-183
INTRODUCTION
Muscles are made up of three types of tissues: Skeletal (focus of chapter) Smooth Cardiac
STRUCTURE OF A SKELETAL MUSCLE
Muscular System is made up of: Individual muscles
(organs) Which are made up of
Skeletal muscle tissue
Nervous tissue Blood Connective tissue
CONNECTIVE TISSUE COVERINGS
Fascia: Separate an individual skeletal muscle from
adjacent muscles and hold it in position Tendon:
Cordlike fascia that extends beyond end of muscle and attaches bone to muscle
Aponeuroses: Sheetlike covering that attaches muscle to
muscle
CONNECTIVE TISSUE COVERINGS CONT.
Epimysium Layer of connective tissue that surrounds a
skeletal muscle Perimysium
Extends inward from epimysium to separate muscle tissue into small compartments
Fascicles: Bundles of skeletal muscle fibers
Endomysium: Covers individual muscle fibers
SKELETAL MUSCLE FIBERS
Each fiber is a single muscle cell that contracts in response to a stimulation and then relaxes when stimulation ends.
SKELETAL MUSCLE FIBERS CONT. Thin elongated cylinder with rounded ends
that extends length of muscle. Surrounded by a Sarcolemma (cell
membrane) Contains Sarcoplasm (cytoplasm) which
contains oval nuclei and mitochondria Sacroplasm also contains Myofibrils
Myofibrils play a fundamental role in contraction
SKELETAL MUSCLE FIBERS CONT. Myofibrils
Contain two kinds of protein filaments Myosin (thick) Actin (thin)
Arrangement of filaments produce light and dark striations or bands
Striation Pattern Two parts:
I bands (light bands) are composed of thin actin filaments and are directly attached to Z Lines
A Bands (dark bands) are composed of thick myosin and overlaps I Bands Central region called H Zone Thickening of Myosin known as M Line
Z line to Z Line make up sarcomere
SKELETAL MUSCLE FIBERS CONT.
Within Sarcoplasm: Sarcoplasmic Reticulum (ER)
Network of membranous channels that surround myofibrils
Transverse Tubules: T-tubules:
Membranous channel that extends inward and passes al the way through to the outside of the fiber. Contains extracellular fluid.
Cisternae: Region where actin and myosin filaments overlap
SR and T-tubules active muscle contraction mechanism when fiber is stimulated.
MEDICAL MINUTE
Muscle fibers and their associated connective tissues are flexible but can tear if overstretched. This type of injury, common in athletes, is called a muscle strain. The seriousness of the injury depends on the degree of damage the tissues sustain. A mild strain injures only a few muscle fibers, the fascia remains intact, and loss of function is minimal. In a sever strain however, many muscle fibers as well as the fascia tear, and muscle function may be completely lost. Such a sever strain is painful and produces discoloration and swelling.
NEUROMUSCULAR JUNCTION
Motor Neuron: Stimulate muscle fibers to contract
Neuromuscular Junction Connection between the motor neuron and
muscle fiber Motor End Plate:
Specialized portion of muscle fiber membrane Branches and projects into recesses of the
muscle fiber membrane Neurotransmitters:
Chemical secretion that stimulates muscle fiber to contract
MOTOR UNITS
One motor neuron and the muscle fibers associated with it constitute a motor unit
SKELETAL MUSCLE CONTRACTION
Contraction is a complex interaction of cell components and biochemicals
Contraction occurs when actin and myosin slide past one another shortening the muscle fiber and pulling on its attachments.
ROLE OF ACTIN AND MYOSIN
Globular portions of myosin filaments can form cross-bridges with actin filaments
Sliding Filament Theory: Calcium ions are present, binding sites on an
actin filament are exposed Cross-bridges on a myosin filament form linkages
at the binding sites A myosin cross-bridge bends slightly, pulling an
actin filament, suing energy from ATP The linkage breaks, The myosin cross-bridge forms a new linkage
with the next binding site
FIG. 8.7 IN TEXT
P. 184
ROLE OF ACTIN AND MYOSIN CONT.
Enzyme ATPase speeds up breakdown of ATP to ADP and phosphate releasing energy.
Energy is needed as a force that causes cross-bridges to pull
Cycle happens over and over as long as ATP is present and the muscle fiber is being stimulated to contract.
Sacromere shortens during contraction
STIMULUS FOR CONTRACTION
Skeletal muscle usually won’t contract without a neurotransmitter stimulating it
Acetylcholine Stimulant that is stored in vesicles at distal ends
of motor neuron Diffuses rapidly across the synaptic cleft and
combines with certain protein molecules (receptors) stimulating a muscle impulse
Travels through T-tubules until it reaches sacroplasmic reticulum
STIMULUS FOR CONTRACTION CONT.
Sarcoplasmic reticulum contains high concentrations of calcium which causes those ions to diffuse into the sarcoplasm.
When sarcoplasm has high concentration of calcium ions they form linkages with actin and myosin filaments and muscle contracts.
STIMULUS FOR CONTRACTION
Two events lead to Relaxation: 1. Acetylcholine rapidly decomposes by enzyme
acetylcholinesterase. Acety……. Prevents a single nerve impulse from
continuously stimulating a muscle fiber 2. Acetylchone breaks down causing stimulus to
fiber to cease. As a result, calcium ions are transported back into sarcoplasmic reticulum decreasing calcium concentration which causes linkage to break consequently causing muscle to relax.
MEDICAL MINUTE
The bacterium Clostridium botulinum produces a poison, called botulinum toxin, that can prevent the release of acetylcholine from motor nerve fibers at neuromuscular junctions, causing a very serious form of food poisoning called botulism. This condition is most likely to result from eating home-processed food that has not been heated enough to kill bacteria in it or to inactivate the toxin. Botulinum toxin blocks stimulation of muscle fibers, paralyzing muscles, including those responsible for breathing. Without prompt medical treatment, the fatality rate for botulism is high.